Evolutionarily different RNA motifs and RNA-protein complexes to achieve selenoprotein synthesis.

A wealth of RNAs or RNA motifs are instrumental in controlling a variety of post-transcriptional or post-translational regulations. In this regard, selenocysteine incorporation in response to a redefined UGA stop codon certainly constitutes an intriguing and fascinating process. Translation elongation factors specialized for selenocysteine are needed to decode UGA selenocysteine codons. Discrimination between UGA selenocysteine and UGA stop codons also necessitates selenoprotein mRNA hairpins, called SECIS, that are internal to the coding frame in eubacteria or contained in the 3' untranslated regions in archaea/eukaryotes. This dichotomy leads to SECIS RNAs with distinct sequences and structures that tether the specialized translation elongation factor in a direct or indirect fashion, depending on the location of the SECIS RNA. The scope of this review is to bring a sharper focus on the SECIS RNA structures and SECIS RNA-protein complexes involved. Obviously, the examples described here highlight once again the versatility in form and function of RNA.